This invention relates generally to key telephone systems, and more particularly concerns simplifications to such systems including reduction in wiring requirements of the station sets.
Key Systems provide direct selection of the desired telephone line, holding capability on any line, visual indicators which show the status of each line (busy, ringing, holding) and an audible signal (ringer) which can be connected to any line. The present methods of key system design accomplish this by connecting a mechanical switch and light array at each station set via a large number of wires to a central unit which contains the common functions, i.e., ring detection, holding and common audible. All control and indication communication between the set and the central unit is accomplished with high level steady state signals on a wire (or pair) per function. In addition the talk path switching is done at the phone all of which introduces great wiring complexity, and to the end that a single pair of telephone wires is finally connected to the telephone circuits in the station set.